Olfactory cues guide mosquitoes toward humans, from which the mosquitoes derive the blood they need to complete ovarian development. In the malaria mosquito, Anopheles gambiae, host-seeking is suppressed or inhibited for about 72 hours after the mosquito takes a blood meal. The molecular basis for this behavior remains unknown, but may be explained by a humoral control mechanism in which the sensitivity of the olfactory system is altered following blood-feeding. In this project, I will examine the hypothesis that down-regulation of specific odorant receptors modifies the host-seeking behavior of female Anopheles gambiae after blood-feeding. Many of the world's most devastating tropical diseases are spread by the bite of an insect. One of these insects, the Anopheles mosquito, is responsible for spreading the malaria parasite. By understanding how Anopheles mosquitoes use chemical cues to find humans, it may be possible to limit the spread of diseases such as malaria by controlling the biting behaviors of these insects.